BMW has revealed another preproduction concept of its upcoming carbon-fiber-intensive i8--this time as a spyder that presages an open-top version of the lightweight gasoline-electric hybrid sports car that is planned to follow its coupe sibling into showrooms in 2014.

Along with previewing plans for an open-top version of the forward-thinking i8, BMW's latest concept is also claimed to provide additional clues to the actual appearance its high-tech sports car will take into production next year.

As with all future BMW i subbrand models, the i8 is based around a lightweight carbon-fiber-reinforced plastic structure clothed in body panels of the same material. Length, width and height are put at 175.2 inches, 75.7 inches and 47.7 inches, respectively.

While sharing the same distinctive front-end look as the coupe--complete with a signature kidney grille that was blanked off to improve overall aerodynamic efficiency and elements of BMW's latest layered surfacing styling treatment--the i8 spyder gets a free-standing windshield and prominent rollover hoops covered by body panels at the rear of the cabin to give it its own visual character.

There is no clear hint as to whether the new car will receive a targa-style removable roof panel, a folding hardtop or a fabric hood in production guise.

Gone are the flamboyant, transparent body sides and doors that adorned the i8 coupe concept. They are replaced by more conventional panels and doors--the latter supporting sloping side windows that integrate with smaller, fixed rear-quarter glass panels. The body-side treatment below the doors, however, remains the same, hinting that it will be reflected on the production car.

The rear also was modified, with a flat bay above the engine enclosed in a transparent cover. It acts as a trunk, offering a wide but shallow stowage space that is occupied by a newly developed BMW electric scooter on the concept car bound for Beijing.

Inside, the snug 2+2 layout of the i8 coupe was ditched in favor of a purer two-seat arrangement, with the rear bulkhead moved forward to provide added space for the engine at the rear of the cabin. With a 104.3-inch wheelbase, interior accommodation is described as "generous."

The heart of the i8 spyder is the same plug-in gasoline-electric hybrid system used by the i8 coupe. It is based around a mid-rear-mounted turbocharged 1.5-liter, three-cylinder direct-injection engine that sends up to 223 hp to the rear wheels.

The same aluminum block engine, which boasts BMW's customary 500-cc individual cylinder capacity to allow it to be produced alongside the company's existing four- and six-cylinder powerplants, is planned to be offered in future Mini models and a new front-wheel-drive, entry-level BMW model, albeit in a milder state of tune.

In the i8 spyder, the combustion unit is supported by a 131-hp electric motor mounted up front within the axle assembly, where it provides drive to the front wheels via a fixed-ratio gearbox. Both the engine and the motor are described as in-house BMW developments and have been tuned to deliver a total system output of 354 hp, together with 406 lb-ft of torque.

Being a full hybrid, the i8 spyder is capable of running on gasoline or electric power, or a combination of the two. It is also capable of running in front-, rear- or four-wheel drive, depending on what power source is in use. Fuel for the gasoline engine is stored in a tank just behind the rear bulkhead, while energy for the electric motor is provided by a lithium-ion battery sited wholly within the center tunnel--a position that BMW says gives its latest concept a 50:50 front-to-rear weight distribution along with a comparatively low center of gravity.

The total recharge time for the battery is 105 minutes using a high-voltage system, according to BMW. A range-extending function that uses the gasoline engine to provide charge to an alternator when energy levels become depleted also allows the i8 spyder to generate its own electrical energy on the run. A recuperation system is also included to collect kinetic energy produced under braking and on a trailing throttle.

With a claimed 3,954-pound weight, BMW says its computer simulations put the i8 spyder's 0-to-62-mph time at 5.0 seconds.

Holding firm to earlier claims made for the i8 coupe, the company also says that it will be able to achieve combined-cycle consumption of up to 78.3 mpg (U.S.) on the existing European cycle--run almost entirely in electric mode to take advantage of loopholes in the procedure. In electric mode, it has a zero-emission range of between 17 and 19 miles depending on ambient temperature and the topography of the road.

Set to be produced at BMW's Leipzig factory in Germany from the third quarter of 2014 onward, the i8 spyder is destined to follow the i8 coupe to showrooms in 2014.